UNIVERSITY   OF   CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL   EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 


LABORATORY  TESTS   OF 
ORCHARD    HEATERS 


A.  H.  HOFFMAN 


BULLETIN  442 

November,  1927 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1927 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/laboratorytestso442hoff 


LABORATORY  TESTS  OF  ORCHARD  HEATERS* 

A.  H.  HOFFMAN  t 


Field  studies  of  the  economic  phases  of  orchard  heating  have  been 
made  by  Young/9' 10'  ll> 12)  Young  and  Cate,(13)  Schoonover,  Hodgson 
and  Young/6)  West  and  Edlefsen/8)  Webber  et  al./7)  Garcia  and 
Fite,(1)  and  others.  Tests  to  determine  the  effectiveness  of  different 
orchard  heaters  to  stay  the  fall  of  temperature  have  been  made  in 
large  number  and  variety  by  Young/9' 10'  11> 12)  West  and  Edlefsen/8) 
(VGara/4)  and  others.  Aside  from  some  measurements  of  radiation 
made  by  Kimball  and  Young/ 3)  exact  measurements  of  the  perform- 
ance of  the  individual  heaters  have  in  general  been  lacking  and  are 
needed  for  the  guidance  of  both  the  user  and  the  manufacturer.  At 
the  urgent  request  of  the  Citrus  Growers '  Department  of  the  Southern 
California  Farm  Bureaus  and  others  the  work  here  reported  was 
undertaken.  In  general  it  has  been  found  that  the  methods  which 
mechanical  engineers  commonly  use  in  testing  the  performance  char- 
acteristics of  steam-boiler  furnaces  and  the  like  are  inapplicable  to 
orchard  heaters  for  the  reason  that  the  latter,  burning  in  the  open, 
present  an  entirely  different  problem.  Hence  it  has  been  found 
necessary  to  devise  new  methods  and  apparatus. 


THE  IDEAL  ORCHARD  HEATER 

Those  who  have  made  the  most  thorough  study  of  the  subject  are 
generally  agreed  that  the  following  characteristics  in  an  orchard 
heater*  are  desirable  for  reasons  obvious  or  specified. 

1.  It  should  be  able  to  burn  fuel  (and  hence  to  produce  heat)  at 
rates  that  will  enable  the  fruit  grower  to  control  the  temperature  of 
his  orchard  within  the  necessary  limits.  The  only  practical  method 
yet  found  for  preventing  frost  damage  in  orchards  is  by  adding  heat 
to  the  air. 

2.  It  should  burn  the  fuel  completely  so  that  all  the  heat  contained 
may  be  liberated. 


*  The  purpose  of  this  bulletin  is  to  make  the  results  of  these  studies  imme- 
diately available  to  the  user  and  to  the  manufacturer  of  orchard  heaters.  The 
test  methods  will  be  explained  in  a  later  publication. 

t  Associate  Agricultural  Engineer  in  the  Experiment  Station. 


4  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 

3.  Its  radiation  above  the  horizontal  plane  should  not  be  excessive. 

4.  The  gases  rising  from  the  stacks  should  be  discharged  at  a  level 
close  to  the  ground  and  should  not  have  too  great  an  upward  velocity 
or  they  may  be  shot  so  high  that  they  may  not  effectively  warm  the 
orchard. 

5.  The  higher  the  temperature  of  the  heater  surfaces  and  of  the 
gases  rising  from  the  stacks  the  greater  will  be  the  rate  of  radiation 
and  the  higher  the  upward  velocity.  It  follows  therefore  that  very 
high  temperatures  are  undesirable  and  that  as  much  cold  air  as 
possible  should  be  mixed  with  the  products  of  combustion  before  they 
are  discharged  from  a  heater. 

6.  An  orchard  heater  should  not  smoke,  since  smoke  is  a  general 
nuisance  to  all  persons  in  the  region.  It  damages  ripe  fruit  by  black- 
ing it  and  rendering  washing  necessary,  and  wastes  a  small  portion 
of  the  heat  content  of  the  fuel. 

7.  All  the  foregoing  desirable  characteristics  should  be  embodied 
in  a  heater  (a)  that  can  be  produced  at  a  reasonable  cost,  (b)  that 
can  be  operated  with  a  minimum  of  skill,  labor  and  care,  (c)  that  will 
have  a  low  up-keep  expense  and  a  satisfactory  length  of  life,  and  (d) 
that  will  burn  available  fuel. 


THE    PROBLEMS   TO    BE    SOLVED 

The  following  items  are  the  principal  objectives  sought  in  this 
study  : 

1.  What  are  the  characteristic  burning  or  fuel  consumption  rates 
of  the  different  heaters? 

2.  How  efficiently  do  they  convert  fuel  into  heat  ? 

3.  What  per  cent  of  the  heat  is  lost  by  radiation  ? 

4.  How  fast  do  the  hot  gases  rise  from  the  stacks  of  the  heaters  ? 

5.  What  temperatures  are  attained  by  the  gases  and  by  the  heater 
surfaces  ? 

6.  How  much  smoke  is  produced  by  each  heater  and  how  may  a 
visible  record  of  the  smokiness  be  obtained? 

7.  What  characteristics  are  necessary  in  a  satisfactory  fuel  for 
orchard  heating? 


Bul.  442] 


LABORATORY    TESTS    OF    ORCHARD    HEATERS 


THE   HEATERS   STUDIED 

A  total  of  nineteen  heaters,  figure  1,  and  table  1,  were  included. 
Extra  stacks  and  "spiders"  for  placing  over  lard-pail  type  to  reduce 
the  burning  rate  (see  Nos.  6s  and  8s  as  typical  spiders)  brought  the 
actual  number  of  heaters  tested  up  to  twenty-six.  Six  of  these  are  of 
the  briquet  or  solid  fuel  burning  type,  two  are  non-distilling,  and 


Fig.  1. — Names  of  the  heaters  tested:  1.  Pomona.  2.  Kittle.  3.  Scheu 
Jumbo  Cone  Louvre.  4.  Scheu  Baby  Cone  Louvre.  5.  Scheu  Double  Stack. 
6.  Bolton.  6s.  Bolton  (with  spider).  7.  Troutman.  8.  Canco.  8s.  Canco  (with 
spider).  9.  Diamond.  10A.  Dunn  (10  in  the  illustration).  IOC.  Dunn  (with 
30-inch  stack;  not  shown).  11A.  Citrus,  9-gal.  low  stack.  11B.  Citrus,  9-gal. 
medium  stack.  11C.  Citrus,  9-gal.  high  stack.  12A.  Citrus,  6-gal.  low  stack. 
12B.  Citrus,  6-gal.  medium  stack.  12C.  Citrus,  6-gal.  high  stack.  13.  Karr. 
14.  Jessen  (large).  15.  Jessen  (medium).  16.  Jessen  (small).  17.  Low  Delivery. 
18.  Baby  Double  Stack.     19.  Citrus  Gas  Flame. 

eighteen  distilling  oil  burners.  Four  additional  heaters  were  received 
too  late  for  test.  Three  of  these  are  Citrus  heaters  and  similar  to 
Nos.  11B,  11C,  and  19.  They  differ  from  those  illustrated  in  that  each 
has  a  baffle  plate  inside  the  reservoir  and  a  filler  tube  and  filler  cap 
in  the  cover,  and  the  one  similar  to  11B  also  has  the  stack  height 
reduced  from  31  inches  to  18  inches.  The  fourth  is  the  new  Scheu- 
National  Jumbo  Cone  Louvre  heater  and  differs  from  heater  No.  3 
of  the  tests  in  the  following  particulars :  weight  18.3  pounds ;  over-all 
height  44  inches;  stack,  height  22%  inches,  top  diameter  7  inches,  bot- 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


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8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

torn  diameter  9  inches.  The  cone  is  larger  at  the  top  than  that  of  No.  3. 
A  self-contained  lighting  cup  is  placed  at  the  top  of  the  down-draft 
tube.  With  the  exception  of  the  Dunn  heater  (no  longer  manufac- 
tured but  many  still  in  use),  all  the  heaters  studied  were  supplied  by 
courtesy  of  the  manufacturers.  In  each  case  the  maker  was  asked  to 
supply  any  directions  for  use  which  he  had  found  necessary  to  give  the 
buyers  of  his  product.  In  the  tests  such  instructions  were  followed 
as  closely  as  possible. 

The  heaters  studied  are  of  three  types  or  classes,  (1)  those  that 
burn  solid  fuel,  especially  briquets,  (2)  those  that  burn  oil  in  a  burner 
separate  from  the  fuel  reservoir,  and  (3)  those  that  burn  oil  within 
the  reservoir  itself.  The  names  in  common  use  for  these  three  types, 
briquet,  non-distilling  oil,  and  distilling  oil,  are  used  in  reporting  this 
work,  although  the  last  two  terms  do  not  seem  entirely  fitting  since 
condensation  is  not  a  feature  in  the  operation  of  either  type.  In  the 
so-called  non-distilling  heater  the  oil  is  metered  through  a  suitable 
device  in  flowing  from  the  reservoir  to  the  burner.  The  fuel  left  in 
the  reservoir  after  a  night's  burning  of  the  heater  is  practically  the 
same  in  quality  as  before  lighting.  In  the  so-called  distilling  type 
heater  the  fire  inside  the  reservoir  causes  the  more  volatile  portions  of 
the  oil  to  be  vaporized  and  burned  first.  Hence,  after  some  hours  of 
burning,  the  oil  remaining  in  the  reservoir  of  such  a  heater  may  be 
considerably  denser  (lower  Baume  number)  than  the  original  fresh  oil. 

Briquet  heaters  are  not  so  easy  to  extinguish  as  the  oil  burners. 
They  are  usually  left  until  the  complete  charge  of  fuel  has  burned  out. 
Though  some  fuel  might  be  saved  by  emptying  the  contents  of  the 
heaters  upon  the  ground,  generally  the  labor  cost  would  be  too  great. 


THE    LABORATORIES    USED 

In  order  that  the  conditions  under  which  the  heaters  were  placed 
during  test  might  be  comparable  with  those  in  practice,  the  laboratory 
chosen  for  the  bulk  of  the  tests  was  a  tilled  field  about  50  yards  wide 
flanked  on  the  east  by  a  deciduous  orchard  and  on  the  west  by  a  vine- 
yard. The  only  building  near  was  a  small  shed  built  to  shelter  the 
necessary  instruments.  Here  the  tests  were  run  at  night  and  only 
when  the  wind  speed,  measured  at  a  height  of  18  feet  10  inches  above 
the  ground  was  less  than  about  5.5  miles  per  hour.  The  speed  at  the 
level  of  the  heaters  was  much  less.  Higher  wind  speeds  caused  too 
great  variations  in  the  burning  rates  and  made  it  impossible  to  obtain 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  9 

satisfactory  measurements  of  the  quantities  under  study.  The  air 
temperatures  during  the  testing  were  not  so  low  as  is  desirable  but 
were  the  best  available  at  Davis.  However,  it  is  believed  that  a 
re-running  of  the  tests  at  temperatures  between  18°  F  and  28°  F 
would  not  change  the  relative  positions  of  the  heaters  as  to  the 
measurements.  Since  colder  air  is  denser  and  therefore  contains  more 
oxygen  per  cubic  foot  it  would  be  expected  that  for  a  given  adjust- 
ment and  kind  of  fuel  a  heater  would  burn  faster  at  the  colder  air 
temperature.  A  test  indicated  that  this  was  true.  An  open  lard-pail 
heater  was  burned  four  times  at  night  and  thrice  in  the  daytime  using 
17  pounds  of  No.  2  oil  (see  table  7)  for  each  test.  The  wind  speeds 
were  nearly  the  same  for  all  tests.  The  average  day  burning  time  was 
3  hours  0  minutes  and  air  temperature  48.7°  F  ;  the  average  night  time 
2  hours  29  minutes  and  air  temperature  36.3°  F.  See  curves ' '  8  (day) ' ' 
and  "8"  in  figure  2. 

In  general  at  least  two  tests  in  the  field  laboratory  were  made  on 
each  heater,  one  at  ''high  adjustment"  and  one  at  ''low  adjustment, 
meaning,  respectively,  about  as  high  as  a  grower  would  ordinarily 
burn  his  heaters  if  he  feared  he  might  not  be  able  to  hold  a  safe  air 
temperature,  and  about  as  low  as  the  heater  could  be  made  to  burn 
properly.  In  some  cases  it  was  found  later  that  adjustments  had  been 
somewhat  too  high  or  too  low.  It  was  not  always  possible  to  re-run 
the  test. 

To  make  sure  that  the  comparative  records  of  smoke  and  of  upward 
velocities  of  the  gases  were  correct  it  was  decided  to  make  a  "normal 
adjustment"  run  indoors  so  that  wind  effects  might  be  entirely  elimi- 
nated. The  indoor  tests  were  made  in  daytime  in  a  large  room  which 
was  ventilated  after  each  test,  the  heaters  being  lighted  and  warmed 
up  outside  and  brought  in  on  a  small  flat-car. 


FUEL  CONSUMPTION    RATES 

From  the  utility  standpoint  the  burning  or  fuel  consumption  rates 
are  of  the  utmost  importance  since  to  produce  heat  in  large  quantities 
is  the  prime  object.  The  heat  produced  equals  the  number  of  pounds 
of  fuel  burned  times  the  heat  content  per  pound,  assuming  complete 
combustion.  The  heat  content  of  a  fuel  is  generally  expressed  in 
British  thermal  units  (abbreviated  B.t.u.)  per  pound.  Its  value  is 
about  20,000  for  oil,  16,000  for  coke,  and  13,000  for  coal.    A  B.t.u.  is 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


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Fig.  2. — Characteristic  burning  rates.  Each  curve,  except  "8"  and  "8 
(day),"  is  the  record  of  a  single  test  on  the  heater  of  the  corresponding  num- 
ber. The  fuel  reservoirs  were  full  at  lighting.  The  only  draft  adjustments,  if 
any,  were  made  immediately  after  lighting.  All  briquet  heaters  were  top 
lighted.  The  deviations  from  smooth  curves  are  due  principally  to  wind 
variations.  Briquet  type  heaters  vary  more  than  the  oil  burners  (curves  1,  9,  9', 
and  13).  Curve  9'  shows  a  typical  case  of  imperfect  lighting  (heater  No.  9). 
The  dotted  line  curve  "8  (day)"  is  the  average  of  three  tests  run  in  daytime 
and  shows  how  higher  air  temperature  slows  the  burning  rate.  Curve  "8" 
is  the  average  of  4  tests  all  run  at  night.  See  figure  1  and  table  1  for  identi- 
fication of  heaters. 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  11 

the  heat  required  to  warm  one  pound  of  pure  water  one  degree  Fahren- 
heit. It  is  comparatively  easy  to  measure  burning  rates.  For  the  field 
tests  the  scales  used  were  sensitive  to  one-fourth  ounce  and  were  set 
into  the  ground  so  that  the  bottom  of  each  heater  was  on  a  level  with 
the  ground  surface.  Readings  of  weights  were  taken  at  30-minute 
intervals  in  the  field  laboratory  and  at  10-minute  intervals  indoors. 
It  was  found  that  the  burning  rates  of  distilling  type  oil  burning,  and 
of  briquet  burning  heaters  were  greatly  affected  by  slight  changes  in 
wind  speed.  The  two  non-distilling  heaters  tested  were  of  course 
unaffected,  since  in  these  heaters  the  fuel  is  metered  into  the  burner; 
however  such  heaters  are  sensitive  to  temperature  effects,  especially 
when  the  oil  used  is  of  such  nature  that  it  thins  rapidly  on  being 
warmed,  for  example,  oils  A,  B,  C,  and  L  in  figure  11  (see  also  table  6). 
The  oil  burning  heaters  have  characteristic  burning  rate  curves,  a 
few  of  which  are  shown  in  figure  2. 

It  should  be  emphasized  that  in  the  tests  in  which  data  for  these 
curves  were  obtained  the  only  draft  adjustments  were  made  imme- 
diately after  lighting.  Also  no  fuel  was  added  during  test.  Frequent 
regulation  is  essential  in  practice  to  secure  the  desired  results.  Gen- 
erally the  adjustment  will  be  for  a  low  burning  rate  at  lighting  when 
only  a  little  heat  is  needed.  Towards  morning  when  the  temperature 
may  tend  to  go  very  low  a  much  higher  burning  rate  may  be  required ; 
this  would  necessitate  re-regulation  and,  in  lard-pail  and  briquet 
heaters,  re-fueling,  or  lighting  of  reserve  heaters.  It  should  be  noted 
that  all  briquet  type  heaters  tested  were  lighted  at  the  top.  Bottom 
lighting  causes  the  fuel  to  burn  out  in  a  shorter  time. 

The  peaks  that  are  found  on  curves  3  and  8  (fig.  2)  at  points  about 
one  hour  after  lighting  are  evidently  caused  by  the  warming  of  the  oil 
and  consequent  more  rapid  vaporization.  The  later  falling  off  of  the 
burning  rates  is  no  doubt  due  to  the  oil  level  becoming  lower  in  the 
reservoirs  and  to  the  fact  that  the  more  volatile  portions  of  the  fuel 
burn  first  leaving  the  heavier,  more  slowly  vaporizing  portions.  In 
some  heaters  clogging  with  soot  undoubtedly  tends  to  slow  the  rate 
of  burning. 

Most  of  the  deviations  from  smooth  curves  are  due  to  the  effects 
of  variations  in  wind  speed  and  air  temperature;  some  may  be  the 
result  of  errors  in  the  readings.  It  will  be  noted  (fig.  2)  that  the 
burning  rates  of  briquet  type  heaters  are  often  much  more  erratic 
than  those  of  the  oil  burners.  The  method  and  skill  used  in  kindling 
and  in  lighting  and  also  the  character  of  the  material  used  for  kindling 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

have  a  considerable  effect  upon  the  promptness  with  which  the  heater 
will  come  up  to  its  maximum  burning  rate  for  a  given  adjustment. 
Curves  9  and  9'  show  variations  that  may  be  expected.  Curve  9'  is 
a  typical  case  of  slow  starting  which  may  be  caused  by  using  too  little 
or  poor  quality  kindling,  by  improper  placing  of  the  kindling,  or  by 
unskillful  application  of  the  oil  from  the  lighting  torch.  For  briquet 
heaters  two  jute  balls  (fig.  3)  filled  with  paraffin  and  placed  under 
the  top  layer  of  briquets  proved  to  be  very  satisfactory  kindling.  No 
deterioration  of  the  kindling  would  occur  even  if  the  unlighted  heater 
were  left  standing  several  years.  Pieces  of  old  automobile  casing  were 
found  to  serve  well  except  for  the  smoke  and  odor.  A  quart  of  dried 
peach  pits  similarly  placed  was  also  satisfactory.  Short  pieces  of 
seasoned  wood  thoroughly  soaked  with  refuse  crank-case  oil  served 
the  purpose  though  they  were  less  pleasant  to  handle. 


Balls  of  Jute  Wait* 

Sta**?t\s<m  Mi\U- 


Fig.  3. — A  satisfactory  kindling  for  briquets.  Balls  of  jute  waste  2y2  inches 
in  diameter  dipped  into  melted  paraffin.  Two  are  placed  under  the  top  layer 
of  briquets.  They  are  unaffected  by  weather  or  time  and  start  readily  when 
lighted  with  fuel  from  a  lighting  torch. 

Another  factor  that  influences  greatly  the  burning  rate  of  a  given 
heater  under  given  conditions  is  the  volatility  of  the  fuel  used.  If 
light  oil  is  used  the  rate  of  burning  will  be  more  rapid. 

In  these  tests  the  briquet  heaters  burned  up  to  nearly  5  pounds  of 
fuel  per  hour  (table  4),  and  the  oil  burning  heaters  up  to  nearly  15 
pounds  per  hour  (table  5).  It  is  understood,  of  course,  that  the  oil 
burning  heaters  other  than  lard-pail  type  could  have  been  adjusted  so 
as  to  consume  at  considerably  more  than  the  highest  rates  given  in  the 
summaries,  but  in  general  it  would  have  been  at  the  penalty  of  higher 
upward  velocities  and  higher  radiation  rates.  Also  such  excessively 
high  adjustment  would  have  greatly  increased  the  smoke  nuisance. 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  13 


FUEL-TO-HEAT  CONVERSION   EFFICIENCY 

To  find  out  how  efficiently  the  several  heaters  converted  fuel  into 
heat  it  was  necessary  to  analyze  the  hot  gases  arising  from  them  to 
find  the  per  cent  of  carbon  monoxide  gas  and  to  determine  the  weight 
of  smoke  (carbon)  per  unit  volume  of  the  hot  gases.  It  was  found 
necessary  to  take  the  samples  of  the  gases  just  above  the  tip  of  the 
flame.  If  taken  too  low,  considerable  amounts  of  unburned  oily  vapors 
and  much  larger  amounts  of  carbon  would  be  drawn.  If  taken  too 
high,  there  was  greater  danger  of  taking  some  fresh  air.  Hence  good 
results  could  be  obtained  only  when  the  wind  was  nearly  still.  Espe- 
cially sensitive  apparatus  was  used  to  determine  the  per  cent  of 
carbon  monoxide.  This  was  in  no  case  found  to  be  greater  than  five- 
hundredths  of  one  per  cent  even  when  the  gas  sample  had  been  taken 
a  little  too  close  to  the  flame.  The  heat  loss  represented  by  the 
unburned  carbon  in  the  smoke  of  some  of  the  smokiest  heaters  was 
only  about  one-tenth  of  one  per  cent  of  the  heat  value  of  the  fuel  used. 
We  must  conclude  therefore  that  the  fuel-to-heat  conversion  efficiency 
of  all  the  heaters  tested  was  practically  100  per  cent.  That  is  to  say, 
the  heaters  tested  got  out  of  the  fuel  used  practically  all  the  heat  there 
was  in  it.  This  takes  no  account  of  fuel  left  unburned  in  the  reservoirs, 
or  else  assumes  that  the  drafts  in  distilling  type  heaters  are  opened 
sufficiently  at  the  last  to  burn  out  completely  the  asphaltic  residues. 
In  practice  this  latter  would  not  usually  be  done  on  account  of  the 
danger  of  warping  and  of  burning  holes  in  the  bottoms  of  the 
reservoirs.  In  the  tests  here  reported  only  fresh  oil  was  used.  In 
practice  it  is  customary  to  add  enough  fresh  oil  to  refill  the  partially 
emptied  reservoirs  after  each  night's  use.  Thus  the  heavier  residues 
may  accumulate.  Cases  have  been  reported  where  from  this  cause  near 
the  close  of  a  long  period  of  freezing  weather  lighting  became  very 
difficult  and  large  quantities  of  tarry  or  asphaltic  matter  were  left 
when  the  fires  would  no  longer  burn  with  the  ordinary  draft  regu- 
lations. (For  further  discussion  of  smoke  measurements  see  p.  17, 
and  of  fuels,  p.  27.) 

RADIATION    FROM    HEATERS 

Heat  that  passes  out  in  straight  lines  from  a  hot  object  as  a  center 
does  not  appreciably  warm  the  air  or  other  medium  through  which 
it  passes.  It  is  only  when  the  heat  ray  strikes  some  opaque  object 
and  is  absorbed  that  it  is  able  to  warm  the  air  in  the  neighborhood. 
For  these  reasons  that  portion  of  the  heat  that  is  radiated  upwards 


14 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


from  an  orchard  heater  is  largely  lost  to  the  sky.  Whatever  heat  is 
radiated  along  lines  that  fall  below  the  horizontal  will  of  course  be 
absorbed  by  the  soil  and  be  effective  in  warming  the  air.  Also  any 
rays  that  strike  leaves,  twigs,  branches,  and  stems  of  trees  would  be 
saved.  Hence  more  of  the  radiant  heat  would  be  lost  in  a  deciduous 
orchard  than  in  a  citrus  grove. 


Fig.  4. — Apparatus  for  measuring  radiation  from  orchard  heaters.  Four 
heaters  placed  on  scales  set  in  an  arc  of  a  circle  were  tested  in  succession  by 
swinging  the  radiometer  from  one  to  another.  Readings  were  taken  at  seven 
positions  from  0°  angle  (horizontal)  up  to  90°  angle  (vertical).  The  radiometer 
was  connected  electrically  to  a  sensitive  galvanometer  in  the  instrument  shelter. 

The  higher  the  temperature  of  the  hot  gases  and  of  the  heater 
surfaces  the  greater  will  be  the  radiation  loss.  Evidently  the  radiation 
rate  will  vary  as  gas  and  surface  temperatures  change.  A  flaming 
heater  radiates  more  than  one  that  is  too  cool  to  emit  light. 

Apparatus  was  devised  for  measuring  the  heat  radiated  above  the 
horizontal  plane  through  the  effective  radiation  centers  of  the  several 
heaters  (fig.  4).  The  total  heat  radiated  upward  was  in  some  cases 
nearly  5  per  cent  of  the  total  heat  in  the  fuel  burned  (see  summaries 
of  night  tests,  tables  4  and  5 ) . 


Bul.  442] 


LABORATORY    TESTS    OF    ORCHARD    HEATERS 


15 


A  number  of  attempts  were  made  to  reduce  the  radiation  loss  by 
the  use  of  screens  of  various  shapes.  All  of  these  proved  effective  in 
some  degree.  The  most  practicable  form  of  radiation  screen  found 
(though  far  from  being  the  most  effective)  was  a  simple  flat  baffle 
plate  placed  a  few  inches  above  the  stack.  Figure  5  shows  graphically 
the  effect. 


Fig.  5. — How  a  deflector  affects  radiation  to  the  sky.  Distances  out  from 
center  are  proportional  to  the  intensity  of  radiation.  The  space  between  the 
two  curves  indicates  roughly  the  heat  saved  by  the  use  of  an  18-inch  square 
deflector  placed  on  a  Scheu  Jumbo  Cone  Louvre  heater  burning  10.63  pounds  of 
No.  1  oil  per  hour. 


UPWARD  VELOCITY  OF  THE  WARM  GASES 

The  warm  gases  rising  from  an  orchard  heater  should  not  rise  too 
rapidly  or  they  may  not  spread  out  horizontally  and  come  to  rest  at 
a  sufficiently  low  level.  If  shot  out  at  high  velocity  and  high  tem- 
perature they  may  instead  "penetrate  the  temperature-equilibrium 
ceiling"  above  the  orchard  and  in  some  degree  become  ineffective  as 
far  as  warming  the  orchard  is  concerned.  Measurement  of  the  upward 
velocity  of  the  hot  gases  was  accomplished  by  use  of  a  high-temperature 
anemometer  especially  designed  and  built  for  the  purpose.  Calibra- 
tion was  made  to  enable  interpretation  of  its  readings  in  terms  of 
feet  per  second.  A  further  study  is  to  be  made  to  find  out  how  high 
gases  starting  at  14  feet  per  second  will  normally  rise  in  an  orchard. 


16 


UNIVERSITY    OF    CALIFORNIA. EXPERIMENT    STATION 


Fig.  6. — High-temperature  anemometer  as  set  ready  for  use  in  out-of-doors 
tests.  This  measures  the  upward  velocity  of  the  hot  gases.  The  revolutions 
are  recorded  electrically  on  the  chronograph  roll  seen  on  the  right. 

Figure  6  shows  the  high-temperature  anemometer  in  position  for 
use  in  a  field  laboratory  test.  In  the  field  tests  the  anemometer  was 
placed  in  line  with  the  center  line  of  the  stack  and  partly  within  the 
top  to  lessen  wind  effects.  In  the  indoor  tests  it  was  placed  as  in 
figure  7,  in  the  region  of  highest  velocity  of  the  gases.    In  a  few  cases, 


Fig.  7. — Anemometer  placing  in  indoors  tests.    The  region  of  highest  velocity 
generally  found  at  about  two  diameters  distance  above  the  stack  in  still  air. 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  17 

especially  of  low  or  medium  stack  heaters,  slightly  higher  velocities 
(and  sometimes  higher  gas  temperatures  also)  were  found  at  low 
burning  rate  adjustment  than  at  higher  adjustment  in  the  same  heater. 
These  apparent  discrepancies  were  in  general  due  to  the  fact  that  the 
column  of  rising  gases  in  some  cases  did  not  fill  the  whole  area  of  the 
stack  but  was  concentrated  in  a  portion  of  the  space.  As  will  be  seen 
in  the  summaries,  tables  2,  3,  4,  and  5,  the  velocities  range  from  less 
than  2.5  feet  per  second  (below  which  the  anemometer  would  not  run 
satisfactorily)  to  about  5  feet  per  second  for  briquet  burning  heaters, 
and  from  the  same  low  limit  up  to  about  14  feet  per  second  for  oil 
burners. 

The  same  flat  baffle  plate  that  was  found  practicable  to  reduce 
radiation  to  the  sky  may  be  used  satisfactorily  above  many  of  the 
heaters  now  in  use.  Its  use  will  stop  the  rapid  rise  of  a  concentrated 
stream  of  high  temperature  gases  and  send  them  out  horizontally  at 
greatly  reduced  speed,  at  the  same  time  mixing  them  more  effectively 
with  the  cold  air.  It  was  found  that  the  upward  velocity  of  the  gases 
from  heaters  Nos.  2  and  17  was  less  than  2.5  feet  per  second  when  the 
regular  baffles  were  in  place  but  about  8  and  6  feet  per  second, 
respectively,  when  the  baffles  were  removed. 


TEMPERATURE  OF  GASES  AND  HEATER  SURFACES 

It  was  found  very  simple  and  easy  to  measure  these  temperatures 
by  use  of  electrical  pyrometers  designed  to  work  at  the  temperatures 
involved.  Measurement  was  made  just  at  the  top  of  the  stacks. 
Luminous  flames  were  found  very  hot,  in  some  cases  running  about 
1400°  F.  The  temperatures  of  the  heater  surfaces  were  found  to  vary 
considerably,  depending  upon  the  distribution  of  the  fires  inside. 
In  briquet  burning  heaters  lighted  at  the  top  large  and  very  irregular 
variations  were  found.  Hot  spots  develop  and  move  as  the  fire  spreads 
through  the  fuel.  As  before  indicated,  excessively  high  surface  tem- 
peratures are  undesirable  because  they  tend  to  increase  radiation 
losses.    They  also  tend  to  cause  rapid  destruction  of  the  heaters. 


SMOKE    FROM    ORCHARD    HEATERS 

While,  as  before  indicated  (under  "Efficiency,"  p.  13),  the  smoke 
from  orchard  heaters  does  not  represent  an  appreciable  heat  loss,  it  is 
nevertheless  a  great  nuisance  to  the  fruit  grower  and  his  helpers  and 
to  everybody  else  within  its  range,  and  does  not  itself  appreciably 
lessen  the  danger  of  frost  damage. (8) 


18 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


In  the  study  of  smoke  two  things  were  sought:  (1)  to  weigh  the 
smoke  in  a  given  volume  of  the  gases  and,  (2)  to  secure  a  visible  record 
by  which  relative  smokiness  might  be  compared.  Some  difficulties 
were  encountered,  but  satisfactory  methods  and  apparatus  were  finally 
evolved.  The  weights  of  smoke  were  found  to  be  exceedingly  small 
(summaries,  tables  2,  3,  4  and  5). 


TABLE  2 

Summary  of  Daytime  Tests  Briquet  Burning  Heaters* 


No. 

Heater 

Fuel 
charge, 
pounds 

Fuel, 
pounds 
per  hr. 

Time  since 
lighting, 

Heat 
in  fuela, 

B.t.u. 
per  hr. 

Maximum 
upward 

velocity15, 
feet  per 
second 

Temper- 
ature of 
gases  t, 
degrees 
F. 

Smoke, 
pound 
per  1000 

Hr. 

Min. 

cu.  ft. 
gas 

1 

24 
20 
17 

2.94 
2.81 
1.41 

1 
2 
5 

00 
00 
20 

39,590 
37,839 
18,987 

4.7 
4  4 

2.7 

690 
305 
485 

.0085 
.0062 

Clear 

9 

19 
13 

3.44 
2.06 

1 
4 

55 
17 

35,281 
27,740 

2.6 
3.0 

600 
415 

Trace 

Clear 

13 

22 

4.31 

2 

00 

58,038 

5.1 

460 

.0145 

14 

Jessen, large 

No 

day 

run 

15 

Jessen,  medium 

No 

day 

run 

16 

Jessen,  small... 

18 
12 

3.28 
1.78 

1 
3 

30 
55 

44,169 
17,477 

Less  than  2 .  5J 
Less  than  2.5 

645 
335 

.0044 
Trace 

*  All  tests  made  indoors  with  No.  3  briquets  (see  table  7). 

a  Product  of  pounds  fuel  per  hour  by  heat  content  per  pound  as  obtained  by  bomb  calorimeter. 
'  Measured  at  region  of  maximum  velocity, 
t  Measured  at  top  of  stack. 
X  Regular  lid  in  place.     Without  lid,  4.8. 

For  making  a  visible  record  of  relative  smokiness  of  all  the  heaters 
the  same  volume  of  gases  for  each,  taken  from  just  above  the  tip  of 
the  flame,  was  passed  at  the  same  rate  through  a  circle  3  inches  in 
diameter  in  the  center  of  a  5-inch  square  of  white  felt.  For  the  speed 
at  which  the  gases  passed  through,  the  felt  used  made  a  practically 
perfect  filter.  Because  of  its  long  bill  or  tube  (for  cooling  the  gases 
before  they  reached  the  felt)  the  device  in  which  the  square  of  felt  was 
clamped  was  termed  the  'smoke  mosquito."  Figure  8  shows  it  in  use 
in  an  indoor  test.  The  record  of  smoke  in  the  out-of-doors  tests  is 
shown  in  figure  9  and  in  tables  4  and  5.  Series  of  records  were  taken 
on  two  briquet  heaters  (Nos.  1  and  14,  fig.  9)  to  show  the  behavior  with 
the  passage  of  time.    Where  in  the  summaries  (tables  2,  3, 4  and  5)  the 


Bul.  442] 


LABORATORY    TESTS    OF    ORCHARD    HEATERS 


19 


TABLE  3 

Summary  of  Daytime  Tests,  Oil  Burning  Heaters* 


No. 

Name  and  type 

Fuel 
charge, 
pounds, 
approx. 

Fuel, 

pounds 

per 

hour 

Heat 

in  fuela, 

B.t.u. 

per  hr. 

Maximum 

upward 

velocity, 

ft.  per  sec. 

Tempera 

ture  of 

gases, 

°F. 

Smoke, 

pound 

per  1000 

cu.  ft.  gas 

2 

Kittle,  non-distilling 

36 

44 

41 

)    32 

>  31 
i    30 

i    35 

i    34 

12 

11 

8 

12 
10 
9 
13 

24 

1     22 

>  31 

1     29 

1    25 

>" 

!" 

1     28 
13 
12 

22 

3.38 

1.97 

3.72 

6.67 

5.44 

3.00 

3.56 

2.91 

3.94 

0.85 

1.56 

5.63 
5.83 
6.04 
1.03 

4.25 

4.50 

3.09 

4.98 

10.78 

2.69 

5.0 
10.0 
3.00 
1.60 
3.94 

66,748 

38,904 

73,463 

131,719 

107,429 

59,244 

70,303 

57,467 

77,807 

16,786 

30,807 

109,838 
115,131 
192,779 
20,340 

83,929 

88,866 

61,021 

98,345 

212,883 

53,122 

98,740 
197,480 
59,244 
31,597 
77,807 

Less  than  2.5 

Less  than  2.5 

Less  than  2.5 

10.9 

11.8 

9.7 

8.0 

6.9 

4.7 
Less  than  2 . 5 

3.5 

4.8 
5.7 

665     \ 

460     j 
715     j 
955     J 
865      f 
645     j 
1,060     j 
655     j 
670      f 
286     f 

Tracef 
.0053f 

17 
17 

3  / 

Low  delivery,  non-distilling . 

Low  delivery,  non-distilling.. 

Scheu  Jumbo  Cone  Louvre, 
distilling 

.0053f 

.0053 

.0107 

Trace 

Trace 

.0044 

Clear 

Clear 

4  < 

Scheu   Baby   Cone   Louvre, 
distilling 

.0124 
.0329 

4  \ 

Scheu   Baby   Cone   Louvre, 
distilling 

.0062 
Trace 

5{ 

Scheu    Double    Stack,    dis- 
tilling  

.0062 
.0071 

'I 

Scheu    Double    Stack,    dis- 
tilling  

Trace 
Trace 

6 

Bolton,  distilling 

.0338 

6s 

7 

Bolton,  spider  on,  distilling... 
Troutman,  distilling 

.0373 
.0115 
.0115 
.0364 

8 

Canco,  distilling -1 

Canco  (spider  on)  distilling... 
Dunn,  distilling 

1,020 
940 

.0409 
.0364 
.0267 
.0249 

8s 
10A 

Less  than  2 . 5 
8.0 
8.8 
7.7 
8.1 
14.1 

6.0 

9.8 

310      f 
1,420      f 

830      \ 
1,160      f 
1,125     | 
1,140      f 

885      1 

1,160     f 

1,115     f 

1,010     f 

1,070     f 

850     / 
I 

.0178 
.0187 
.0275 

lOCf 

Dunn,  with  30'  x  6'  stack, 
distilling 

.0249 
.0364 
.0382 

11AJ 

Citrus,  9-gal.,  low  stack,  dis- 
tilling  

.0151 
.0124 

HBf 

Citrus,  9-gal.,  medium  stack, 
distilling 

.0187 
.0222 

ncj 

Citrus,  9-gal.,  high  stack,  dis- 
tilling  

.0293 
.0213 

12Af 

Citrus,  6-gal.,  low  stack,  dis- 
tilling  

.0231 
.0258 
.0258 

12B( 

Citrus,  6-gal.,  medium  stack, 
distilling 

.0258 
.0187 
.0240 

12C( 

Citrus,  6-gal.,  high  stack,  dis- 
tilling  

.0115 

4.3 
6.3 
4.0 

.0142 

18 
18 
19 

Baby  Double  Stack,  distilling 
Baby  Double  Stack,  distilling 
Citrus  Gas  Flame,  distilling  . 

Trace 
.0178 
Clear 
Clear 
Trace 
Trace 

*  All  tests  made  indoors  with  No.  2  oil  (see  table  7). 

a  Product  of  pounds  fuel  per  hour  by  heat  content  per  pound  of  fuel  as  obtained 

t  Determinations  of  smoke  density  were  sometimes  made  in  duplicate  or  in  tri 


by  bomb  calorimeter, 
plicate. 


20 


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LABORATORY    TESTS    OF    ORCHARD    HEATERS 


23 


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"smoke,  pound  per  1000  cu.  ft.  of  gas"  is  given  as  "clear,"  no  sign 
of  smoke  was  visible  on  the  felt.  Where  "trace"  is  recorded  a  faint 
circle  was  visible  but  the  quantity  caught  was  too  small  to  be  weighed. 
In  the  indoors  tests  a  pair  of  smoke  records  were  taken  in  the  test 
of  each  heater.  Figure  10  shows  these  pairs  and  indicates  how  closely 
the  smoke  records  check.  The  conditions  of  burning  rates,  etc.,  when 
the  indoors  smoke  records  were  taken,  may  be  found  in  tables  2  and  3. 


Fig.  8. — The  "smoke  mosquito"  in  use.  A  measured  volume  of  the  gases 
is  drawn  from  just  above  the  tip  of  the  flame  through  a  square  of  white  felt. 
Note  pyrometer  (left)  measuring  the  temperature  of  the  gases. 


In  practically  all  the  heaters  clearer  burning  was  obtained  at  low 
burning  rates  than  at  high.  Nearly  all  oil  burning  heaters  smoked 
badly  when  burned  at  maximum  capacity.  A  comparative  study  of  all 
the  heaters  tested  indicated  that  in  some  cases  a  very  slight  difference 
in  design  apparently  caused  a  large  difference  in  smokiness.  While 
absolute  smokelessness  under  all  conditions  seems  not  feasible  under 
present  conditions  of  available  fuel  and  equipment,  still  a  great 
improvements  could  be  made  by  the  elimination,  especially  in  the 
citrus  growing  districts,  of  the  lard-pail  and  all  other  open  type 
heaters ;  by  redesign  of  some  of  the  other  heaters ;  by  more  care  in  the 
production  of  the  fuels  used ;  and  especially  by  more  care  on  the  part 
of  the  user  to  regulate  more  frequently  and  to  avoid  burning  at  too 
high  rates.  In  justice  to  the  user  it  should  be  added  that  poorly 
designed  or  constructed  heater  covers  sometimes  make  it  impossible  to 
regulate  the  burning  rate. 


Bul.  442] 


LABORATORY    TESTS    OF    ORCHARD    HEATERS 


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26 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


EFFECT  OF  ORCHARD   HEATING  ON  THE   PUBLIC   HEALTH 

Considerable  complaint  has  been  heard  that  gaseous  products 
injurious  to  the  health  of  residents  in  the  citrus  growing  districts 
are  given  off  by  the  heaters.  Bronchial  and  pulmonary  affections 
apparently  caused  by  the  smoke  or  by  the  gases  have  been  mentioned 
repeatedly.  No  exhaustive  study  of  this  matter  was  made  but  the 
following  facts  are  determined.  Comparison  with  data  given  by 
Henderson,  Haggard,  Teague,  Prince  and  Wunderlich(2)  and  by 
Sayers,  Meriwether  and  Yant(5)  of  the  U.  S.  Bureau  of  Mines  shows 


Fig.  10. — Smoke  records,  indoor  tests.  At  least  2  daytime  tests  were  made  on 
each  heater ;  note  the  close  agreement  between  the  records  in  each  pair.  The  same 
fuels  (No.  2  oil  and  No.  3  briquets)  were  used  for  all  the  indoor  tests.  Wind 
effects  were  eliminated  in  this  portion  of  the  test  by  running  indoors.  See  tables 
2  and  3  for  rates  of  fuel  consumption,  etc. 


that  the  per  cent  of  carbon  monoxide  given  off  by  orchard  heaters  is 
too  small  to  produce  any  appreciable  effect.  In  fact  very  much  higher 
concentrations  of  carbon  monoxide  are  found  where  automobile  traffic 
is  heavy  in  some  of  the  streets  of  our  cities  than  would  ever  be  present 
under  the  worst  conditions  in  a  heated  orchard.  Some  of  the  fuels 
sold  for  orchard  heating  in  this  state  are  rather  high  in  sulphur 
content  (table  7).  This  sulphur  is  almost  completely  . ' anged  to 
sulphur  dioxide,  a  gas  which,  while  not  dangerous  to  the  same  degree 
as  carbon  monoxide,  is  very  disagreeable  and  irritating  to  the  nasal 
passages,   throat  and  lungs.     No  method  was  found  to   determine 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  27 

whether  smoke  of  itself  had  any  effect  upon  the  health.  Removal  of 
sulphur  from  the  fuels  sold  for  orchard  heating  would  certainly  be 
highly  desirable.  Along  with  this,  of  course,  should  go  reduction  of 
smoke  to  a  minimum. 


FUELS   USED   IN   ORCHARD   HEATERS 

Various  complaints  have  been  made  concerning  the  oils  sold  for 
orchard  heating  purposes  in  this  state.  Several  samples  of  orchard 
heater  oils  were  secured  and  subjected  to  such  tests  as  seemed  likely 
to  indicate  how  satisfactory  they  might  prove  in  use.  Since  usually 
in  non-distilling  heaters  the  rate  at  which  the  oil  will  run  through  a 
small  opening  determines  the  burning  rate,  tests  of  viscosity  were 
made  on  eleven  oils   (table  6).     The  California  residue  test   (later 


TABLE  6 

Oils  Tested  for  Viscosity  and  Per  Cent  of  Eesidue* 


No. 

Source 

Residue,  by 

California  test, 

per  cent 

1 

6.83 

2 

0.201 

3 

0.206 

A 

0.924 

B 

0.935 

c 

1.206 

D 

0.277 

E 

0.639 

K 

0.741 

L 

2.586 

M 

small) 

*  All  from  1925-26  season  supply.    The  viscosities  are  given  in  figure  11. 

described)  was  also  made  and  the  results  for  some  of  the  oils  compared 
with  results  obtained  for  the  same  oils  by  use  of  the  regular  Conradson 
carbon  test  .and  Holde  hard  asphalt  test.  Figure  11  shows  graphically 
the  results  of  the  viscosity  tests.  Evidently  the  samples  that  show 
nearly  straight  vertical  lines  (that  is,  that  maintain  their  free  flowing 
character  almost  constant  from  100°  F  down  to  well  below  the  freezing 
temperature  of  water)  would  run  satisfactorily  in  a  non-distilling  type 
heater.  On  the  other  hand  an  oil  like  C,  B,  or  L,  if  lighted  and  the 
burning  rate  properly  adjusted  at  25°  F,  would  flow  very  much  faster 
after  the  fuel  in  the  reservoir  came  up  to  35°  F  or  40°  F.  Oil  A  was 
solid  at  12°  F  and  oil  L  at  16°  F.  Oil  L  would  hardly  flow  at  all 
below  25°  F. 


28 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 


To  study  the  effect  of  settling,  two  samples  of  oil  No.  1  were  taken, 
one  from  the  top  and  the  other  from  the  bottom  of  a  50-gallon  drum 
after  it  had  stood  undisturbed  for  three  weeks.  The  bottom  oil  was 
found  to  be  0.5°  Beaume  heavier  than  the  top,  but  both  showed  the 
same  viscosity  curve  as  that  of  the  composite  sample  of  oil  No.  1. 
Possibly  longer  settling  might  have  made  a  noticeable  difference.  Also 
other  oils  might  have  behaved  differently.  Oil  No.  1  was  chosen 
principally  because  it  was  very  dark  in  color  and  on  being  burned  left 
much  asphaltic  residue. 


\//scos/ties  or 

O&chard  Heater  O/ls 

J 925 '-'26  Reason 


SO  120  160 

Viscosity,   Seconds  Soybolt 

Fig.  11. — As  the  oils  thicken  on  becoming  colder,  longer  times  are  required 
for  a  standard  unit  quantity  of  oil  to  flow  through  the  standard  opening  in  the 
Saybolt  test  apparatus.  The  straighter  lines  show  oils  that  thicken  less  rapidly 
on  cooling.    See  table  6. 

The  accumulation  of  heavy  residues  in  the  reservoirs  of  distilling 
type  heaters  and  in  the  burners  of  the  non-distilling  type  has  been  a 
frequent  cause  of  trouble.  In  extreme  cases  the  heaters  would  operate 
very  unsatisfactorily  or  could  scarcely  be  made  to  burn  at  all.  It 
seems  that  these  asphaltic  residues  are  not  necessarily  merely  so  much 
asphalt  that  was  present  in  the  original  oil,  but  are  probably  produced 
by  what  the  oil  chemist  calls  ' '  cracking  of  the  molecules ' '  of  oil  when 
heated.  In  the  "cracking"  process  a  molecule  of  the  oil  may  be 
regarded  as  breaking  up  and  then  reassembling  it  component  parts  to 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  29 

make  two  new  molecules  different  from  each  other  and  from  the 
original  molecule.  Thus  the  heat  to  which  the  oil  in  the  reservoir  is 
subjected  may  change  some  of  the  oil  into  two  new  kinds  of  oil,  one 
that  vaporizes  easily  and  therefore  burns  readily,  and  one  that  is  very 
heavy  and  hard  to  vaporize  and  hence  is  liable  to  fail  to  mix  with  the 
oxygen  of  the  air  and  so  be  left  unburned.  Some  oils  will  "crack" 
much  more  readily  than  others. 

An  attempt  was  made  to  find  a  simple  test  that  would  show 
whether  a  given  oil  would  "crack"  badly  or  not.  The  apparatus  used 
consists  of  a  sheet  copper  burner  bowl  A  (fig.  12),  a  pedestal  B  on 


Fig.  12. — California  residue  test  for  orchard  heater  oils.  Ten  grams  of  the 
oil  to  be  tested  is  placed  in  bowl  A.  Bowl  is  placed  on  pedestal  B  and  draft 
pipe  C  placed  over  as  in  figure  13.  Lighting  is  by  an  alcohol  swab  burned 
under  one  edge  of  the  bowl.  The  residue  remaining  when  the  fire  dies  is 
weighed.     See  data  in  tables  6  and  7. 

which  to  support  it,  and  a  draft  pipe,  C.  A  10-gram  sample  of  oil  is 
weighed  in  the  burner  bowl,  the  bowl  placed  level  on  the  pedestal  and 
the  draft  pipe  placed  over  it  (fig.  13) .  Lighting  is  accomplished  by  the 
use  of  a  swab  soaked  in  alcohol  burned  under  one  edge  of  the  bowl 
until  the  fuel  ignites.  A  pasteboard  screen  to  prevent  air  currents  is 
placed  around  the  apparatus.  When  the  fire  dies  out  the  residue  is 
found  by  weighing  the  bowl  on  a  sensitive  analytical  balance.  Table  7 
gives  the  results  obtained  on  the  oils  used  in  the  heater  tests  and  a  few 
other  oils,  together  with  results  of  other  standardized  tests  for  oils. 
It  will  be  noted  that  there  is  a  rather  close  parallel  between  the  new 
California  residue  test  and  the  Conradson  carbon  and  Holde  hard 
asphalt  tests.  Since  the  per  cents  of  residue  are  considerably  larger 
in  the  new  test  than  in  the  Conradson,  higher  accuracy  should  be 
obtained  by  the  California  test,  with  the  same  degree  of  care  and 
sensitiveness  of  instruments.  The  Conradson  test  results  given  were 
obtained  from  two  companies  engaged  in  commercial  oil  testing.  It 
will  be  noted  that  the  results  differ  somewhat.  The  Holde  tests  were 
made  by  the  Chemistry  Division  staff  at  Davis. 


30 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


A  very  simple  test  with  inexpensive  apparatus  (fig-.  14)  may  be 
made  by  the  rancher  himself  to  try  orchard  heater  oils  for  residue. 
This  is  a  modification  of  the  California  test  but  is  less  accurate  and 
gives  only  a  visual  instead  of  a  numerical  comparison.  However,  the 
results  obtained  are  sufficiently  definite  for  all  ordinary  purposes. 


Fig.  13  Fig.  14 

Fig.  13. — California  residue  test  apparatus  (assembled).  When  in  use,  a 
pasteboard  screen  (not  shown)  surrounds  the  apparatus  to  reduce  the  effects 
of  air  currents.  The  balance  shown  is  used  to  weigh  the  10  grams  of  oil.  A 
delicate  analytical  balance  is  used  for  the  bowl  and  residue. 

Fig.  14. — Modified  form  of  California  residue  test  apparatus.  This  enables 
making  a  residue  test  without  expensive  or  delicate  apparatus.  Half-pint 
samples  of  the  oils  are  burned  in  small  tin  pans  and  the  residues  compared. 

Equal  volumes  (%  pint)  or  equal  weights  (%  lb.)  are  taken  of 
the  several  oils  to  be  tested.  Instead  of  the  small  copper  burner  A  of 
figure  12,  an  ordinary  tin  pan  5%  inches  inside  diameter  at  the  top, 
4^/2  inches  at  the  bottom  and  1%  inches  deep  is  used.  It  is  well  to 
have  as  many  pans  as  there  are  oils  to  be  tested,  so  that  the  results 
may  be  kept  for  comparison.  An  empty  tomato  can  placed  bottom 
end  up  may  be  used  as  a  pedestal.  The  draft  tube  is  not  necessary. 
The  oil  may  be  lighted  by  placing  a  2-inch  diameter  asbestos  swab 
soaked  in  torch  oil  (gasoline  and  kerosene  equal  parts)  under  an  edge 
of  the  pan.  If  preferred  the  pan  of  oil  may  be  heated  on  top  of  a 
stove  until  it  will  ignite  readily  when  a  lighted  match  is  applied. 


BUL.  442]  LABORATORY   TESTS   OF    ORCHARD    HEATERS 


31 


Fig.  15. — Residues  from  orchard  heater  oils  obtained  by  use  of  the  apparatus 
shown  in  figure  14.  Upper,  oil  No.  1  unsatisfactory;  lower,  oil  No.  2  more 
satisfactory. 


32  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

After  lighting,  a  screen  to  keep  off  air  draughts  should  be  placed 
around  if  the  test  is  made  out-of-doors.  A  carton  about  2  feet  square 
and  3  feet  high  from  which  the  top  and  bottom  have  been  removed 
makes  a  satisfactory  screen. 

An  unsatisfactory  oil  will  leave  a  residue  that  is  very  noticeable 
though  it  may  weigh  less  than  half  an  ounce.  Usually  such  a  residue 
will  consist  of  two  parts,  a  thin  layer  of  black,  shiny,  asphaltic 
material  on  the  bottom  of  the  pan,  and  above  it  a  hard,  flaky  crust 
consisting  mostly  of  carbon.  A  satisfactory  oil  will  have  no  noticeable 
asphaltic  residue  and  very  little  of  the  crusted  carbon. 

Since  the  temperature  of  the  pan  and  contents  during  the  burning 
determines  in  a  large  measure  how  much  residue  will  be  left,  it  is 
essential  that  all  the  conditions  that  might  affect  this  temperature 
should  be  alike  in  all  tests,  if  the  results  are  to  be  compared.  This 
refers  especially  to  the  method  of  lighting  and  the  level  placing  on  the 
pedestal.  Using  an  asbestos  pad  between  the  burner  pan  and  the 
pedestal  in  some  of  the  tests  and  not  in  the  rest,  would  make  the  results 
of  doubtful  value.  Differences  of  5°  F  or  10°  F  in  the  air  tempera- 
tures when  the  tests  are  run  will  not  appreciably  affect  the  results. 
Figure  15  shows  the  residues  obtained  by  this  test  on  oils  Nos.  1  and  2 
(for  other  data  of  these  oils  see  table  7).  Oil  No.  1  produced  quite  a 
drip  of  asphaltic  material  from  the  burners  of  the  non-distilling  type 
heaters  tested.  At  intervals  the  crusted  carbon  left  in  the  burners  by 
this  oil  had  to  be  removed.  Oil  No.  2  burned  much  more  satisfactorily. 
The  briquets  used  were  in  general  satisfactory.  The  sulphur  fumes 
were  noticeably  worse  from  the  coal  dust  briquets  as  would  be  expected 
from  the  high  sulphur  content  (table  7).  The  relatively  large  ash 
residues  from  the  coal  dust  briquets  sometimes  partially  clogged  the 
grates  and  so  reduced  the  burning  rates.  The  coke  and  carbon 
briquets  used  had  less  sulphur  and  left  no  noticeable  ash.  They  were 
however  less  satisfactory  to  handle  because  of  their  tendency  to 
blacken  anything  they  touched  and  to  break  into  pieces. 

Comparison  of  California  residue  test  results  with  specific  gravities 
(table  7)  shows  that  the  latter  do  not  give  any  indication  of  the 
probable  behavior  of  an  oil  with  respect  to  asphaltic  residue. 

It  was  found  that  the  asphaltic  residues  from  some  oils  collected  in 
and  under  the  burners  of  the  non-distilling  heaters  tested.  Sometimes 
these  residues  spread  over  the  ground  around  the  heater.  "With  some 
oils  at  certain  adjustments  the  residues  burned  out  automatically  at 
intervals  or  could  be  made  to  burn  out  without  apparent  harm  to  the 
heater  by  applying  a  little  fuel  from  the  lighting  torch  to  the  base  of 
the  burner.     The  residues  resulting  from  "cracking"  of  the  fuel  and 


Bul.  442] 


LABORATORY    TESTS    OF    ORCHARD    HEATERS 


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co   to   to   ©   ©   ©   © 

Resid 
(Cali 
test) 

per  ce 

CO    00    00    h-    to    to    OO 

O)  w  o  *  o  o  w 

>k      OS      H- 

B  -     «>c 

c*- 

re 

34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

from  droppings  of  soot  that  accumulated  in  the  reservoirs  of  the  dis- 
tilling heaters  tested  could  be  burned  out  in  many  cases  by  opening 
the  drafts  wide.  Very  high  temperatures  in  the  reservoirs  would 
result.  Whether  this  would  rapidly  destroy  the  heaters  by  burning 
out  the  bottoms  was  not  determined  by  these  tests.  Growers  report 
that  reservoirs  frequently  burn  through  at  the  bottom  of  the  down- 
draft  tubes.  No  intensive  study  of  orchard  heater  troubles  was  made 
in  connection  with  the  laboratory  tests  here  reported.  In  general  the 
test  runs  were  of  too  short  duration  for  characteristic  troubles  to 
develop  fully.  It  is  believed  that  these  can  be  studied  more  satisfac- 
torily in  field  tests  such  as  are  reported  by  Schoonover,  Hodgson, 
and  Young. (6) 

It  was  found  that  refuse  oil  drained  from  crankcases  of  auto- 
mobiles and  tractors  could  be  burned  satisfactorily  in  several  distilling 
type  heaters. 

CAUTION    NECESSARY   IN    USE   OF   DATA 

It  is  inadvisable  to  draw  hard  and  fast  conclusions  as  to  the 
relative  merits  and  demerits  of  the  several  heaters  tested,  using  as  a 
basis  of  comparison  the  data  given  in  the  summaries.  This  is  particu- 
larly the  case  where  the  quantities  measured  were  themselves  very 
small.  It  should  be  remembered  that  the  smaller  the  quantity,  the 
less,  in  general,  will  be  the  degree  of  accuracy  to  which  it  can  be 
measured.  Also  it  should  be  borne  in  mind  that  the  quantities 
measured  were  often  changing  appreciably  from  moment  to  moment. 
It  was  not  in  every  case  possible  to  take  and  to  average  a  large  number 
of  readings  for  the  reason  that  limited  time  was  available  when 
weather  conditions  were  fit  for  making  the  tests.  Nevertheless  the  data 
presented  enable  the  making  of  a  fair  general  comparison. 


SUMMARY 

New  methods  of  testing  were  necessary  because  those  used  by 
mechanical  engineers  for  testing  furnaces  were  found  inapplicable. 
Full  description  of  methods  is  to  be  made  in  a  later  publication. 

Nineteen  heaters  were  studied  and  each  was  given  a  high  and  a 
low  test  in  the  open  and  a  " normal"  test  indoors. 

The  burning  rate  was  found  important  since  it  governs  the  rate 
of  heat  production.  Each  type  of  heater,  if  left  without  readjust- 
ment, was  found  to  have  a  characteristic  burning  rate  curve  the  shape 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  35 

of  which  was  altered  by  changes  in  wind  speed  and  air  temperature 
and  in  temperature  and  volatility  of  the  fuel.  The  burning  rate  is 
adjustable  in  most  heaters.  Too  high  a  rate  was  found  undesirable 
since  it  tends  to  increase  smoke  and  losses  by  radiation  and  by  gases 
rising  too  high.  It  also  tends  to  cause  rapid  scaling  off  and  destruc- 
tion of  the  stacks.  Frequent  and  careful  regulation  is  highly  desirable 
as  a  means  of  overcoming  the  smoke  nuisance  as  well  as  of  securing 
the  desired  heat  production. 

It  is  customary  in  many  orchards  to  light  only  a  portion  of  the 
heaters  at  first  and  light  others  as  the  night  grows  colder.  From  the 
standpoint  of  heat  distribution  and  reduction  in  the  amount  of  smoke 
it  is  better  to  light  all  of  the  heaters  and  burn  them  at  a  low  rate  with 
frequent  regulation.  This  frequent  regulation  will  control  the  burn- 
ing rates  of  the  heaters  in  such  a  way  as  to  save  considerable  fuel. 
With  briquet  heaters  the  most  practical  way  of  controlling  the  burning 
rate  is  to  start  with  a  relatively  small  fuel  charge  and  refuel  at  about 
two-hour  intervals  throughout  the  night, 

All  the  heaters  were  found  practically  100  per  cent  efficient  from 
the  standpoint  of  converting  fuel  into  heat,  there  being  almost  no 
carbon  monoxide  in  the  gases  and  the  heat  lost  in  the  unconsumed 
carbon  of  the  smoke  being  in  every  case  less  than  one-tenth  of  one 
per  cent  of  the  total  heat  in  the  fuel  used. 

The  heat  radiated  above  the  horizontal  plane  ranged  from  about 
one  to  nearly  five  per  cent  of  the  total  heat  in  the  fuel.  Not  all  of  this 
radiated  heat  is  lost.  The  portion  that  strikes  leaves,  twigs,  or  other 
opaque  objects  and  is  absorbed  serves  to  warm  the  air.  Baffles  for 
decreasing  the  radiation  loss  were  found  practicable. 

High  upward  velocities  and  high  temperatures  tend  to  waste  fuel 
by  sending  the  hot  gases  to  high  levels  above  the  orchard.  The 
velocities  found  were  satisfactorily  low  except  in  high  stack  heaters  not 
equipped  with  a  horizontal  baffle  plate.  In  some  of  these  velocities 
as  high  as  14  feet  per  second  were  found. 

Smoke  is  always  a  nuisance  and  of  little  or  no  benefit  as  a  blanket 
to  prevent  radiation.  The  lard-paid  heaters  were  the  worst  offenders. 
A  number  of  the  later  oil  burners  were  practically  smokeless  when 
burned  at  normal  and  low  rates,  but  all  smoked  some  when  burning  at 
very  high  rates.  Satisfactory  control  of  the  burning  rate  was  in  some 
cases  made  difficult  if  not  quite  impossible  by  ill-fitting  reservoir 
covers  in  distilling  type  heaters.  Briquet  heaters  smoke  considerably 
at  lighting  and  for  a  time  afterward  but  become  clearer  as  burning 
progresses.    Photographic  smoke  records  were  made. 


36  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

No  exhaustive  study  was  made  of  orchard  heater  gases  and  smoke 
as  affecting  the  public  health.  The  concentrations  of  carbon  monoxide 
are  evidently  too  small  to  cause  appreciable  effects.  Sulphur  dioxide 
apparently  caused  annoyance  to  some  of  the  workers.  What  part  the 
smoke  itself  played  was  not  determined. 

Oils,  being  higher  in  heat  content  per  pound,  are  more  effective 
than  solid  fuels.  The  oils  sold  for  orchard  heating  differ  considerably 
in  characteristics  that  affect  their  suitability.  Oils  that  leave  large 
asphaltic  residues  on  burning  are  less  desirable  both  for  distilling 
and  for  non-distilling  type  heaters.  A  new  method  for  determining 
per  cent  of  residue  is  described.  High  sulphur  content  is  objectionable. 
High  viscosity  and  rapid  increase  in  viscosity  when  temperature 
decrease  make  an  oil  unsuitable  for  non-distilling  type  heaters. 


ACKNOWLEDGMENTS 

The  author  wishes  to  express  his  grateful  appreciation  of  advice 
and  assistance  received  from  his  colleagues  and  from  many  others. 
Especial  mention  should  be  made  of  E.  Ower,  A.  C.  G.  I.,  of  the  British 
National  Physical  Laboratory  who  furnished  unpublished  data  that 
enabled  the  calibration  of  the  high-temperature  anemometer ;  Professor 
L.  B.  Spinney  of  the  Iowa  State  College  and  Dr.  W.  W.  Coblentz  and 
others  of  the  U.  S.  Bureau  of  Standards  who  made  valuable  sugges- 
tions concerning  the  measurement  of  radiation ;  Dr.  C.  S.  Bisson  of  the 
University  of  California  who  directed  the  chemical  work;  Dr.  W.  L. 
Howard,  Professors  R.  W.  Hodgson  and  A.  H.  Hendrickson  of  the 
University  of  California,  Mr.  Floyd  D.  Young  of  the  U.  S.  D.  A. 
Weather  Bureau,  and  the  members  of  the  Research  Committee  of  the 
American  Society  of  Agricultural  Engineers,  who  criticized  the 
original  plan  of  the  work  and  read  the  manuscript.  I  am  especially 
indebted  to  Mr.  W.  R.  Schoonover  of  the  University  of  California  for 
a  large  number  of  practical  suggestions  for  the  orchardist  which  are 
made  a  part  of  this  bulletin. 


BUL.  442]  LABORATORY   TESTS   OF   ORCHARD    HEATERS  37 


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STATION  PUBLICATIONS  AVAILABLE  FOE  FREE   DISTRIBUTION 


No. 

253.  Irrigation  and  Soil  Conditions  in  the 
Sierra   Nevada   Foothills,    California. 

262.  Citrus  Diseases  of  Florida   and   Cuba 

Compared   with    those   of   California. 

263.  Size  Grades  for  Ripe  Olives. 

268.   Growing  and  Grafting  Olive  Seedlings. 

273.  Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain,  Fresno 
County,    California. 

276.  The  Pomegranate. 

277.  Sudan    Grass. 

278.  Grain    Sorghums. 

279.  Irrigation   of  Rice  in   California. 
283.  The  Olive  Insects  of  California. 
294.   Bean   Culture  in    California. 

304.  A  Study  of  the  Effects  of  Freezes  on 

Citrus    in    California. 
310.  Plum    Pollination. 
312.  Mariout  Barley. 
813.   Pruning      Young      Deciduous      Fruit 

Trees. 
819.  Caprifigs    and    Caprification. 
824.   Storage  of  Perishable  Fruit  at  Freez- 
ing Temperatures. 
325.  Rice     Irrigation     Measurements     and 

Experiments   in    Sacramento   Valley, 

1914-1919. 
328.  Prune   Growing   in    California. 
331.  Phylloxera-Resistant    Stocks. 
835.   Cocoanut   Meal    as    a    Feed    for   Dairy 

Cows  and   Other  Livestock. 
339.  The    Relative    Cost    of    Making    Logs 

from   Small  and  Large  Timber. 
840.   Control     of     the     Pocket     Gopher     in 

California. 

343.  Cheese    Pests    and    Their    Control. 

344.  Cold    Storage   as   an    Aid   to   the   Mar- 

keting of  Plums. 

346.  Almond    Pollination. 

347.  The  Control  of  Red  Spiders  in  Decid- 

uous Orchards. 

348.  Pruning  Young  Olive  Trees. 

349.  A    Study    of    Sidedraft    and    Tractor 

Hitches. 

350.  Agriculture      in      Cut-over      Redwood 

Lands. 

353.  Bovine   Infectious   Abortion. 

354.  Results  of  Rice  Experiments  in   1922. 

357.  A    Self-mixing    Dusting    Machine    for 

Applying      Dry       Insecticides       and 
Fungicides. 

358.  Black    Measles,     Water    Berries,     and 

Related  Vine  Troubles. 
861.   Preliminary    Yield    Tables    for    Second 
Growth   Redwood. 

362.  Dust  and  the  Tractor  Engine. 

363.  The  Pruning  of  Citrus  Trees  in  Cali- 

fornia. 

364.  Fungicidal    Dusts    for    the    Control    of 

Bunt. 

365.  Avocado  Culture  in   California. 

366.  Turkish  Tobacco  Culture,   Curing  and 

Marketing. 

367.  Methods  of  Harvesting  and  Irrigation 

in   Relation  of  Mouldy  Walnuts. 

368.  Bacterial  Decomposition  of  Olives  dur- 

ing  Pickling.    • 

369.  Comparison     of     Woods     for     Butter 

Boxes. 

370.  Browning  of  Yellow  Newtown  Apples. 

371.  The    Relative    Cost   of    Yarding    Small 

and   Large   Timber. 

373.  Pear    Pollination. 

374.  A  Survey  of  Orchard  Practices  in  the 

Citrus    Industry  of    Southern    Cali- 
fornia. 

375.  Results    of   Rice    Experiments    at   Cor- 

tena,    1923. 

376.  Sun-Drying  and  Dehydration  of  Wal- 

nuts. 

377.  The  Cold    Storage  of   Pears. 
379.  Walnut   Culture   in   California. 


BULLETINS 
No. 


380. 
382. 


385. 
386. 


387. 
388. 


389. 
390. 


391. 
392. 


394. 


395. 
396. 


397. 


398. 
399. 


400. 
401. 

402. 
404. 
405. 
406. 
407. 


408. 
409. 


410. 
411. 


412. 


415. 
416. 


417. 
418. 


419. 
420. 


421. 
422. 


423. 
424. 


425. 
426. 


427. 

428. 


429. 


Growth  of  Eucalyptus  in  California 
Plantations. 

Pumping  for  Drainage  in  the  San 
Joaquin    Valley,    California. 

Pollination    of    the    Sweet   Cherry. 

Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig  Smut. 

The  Principles  and  Practice  of  Sun- 
drying  Fruit. 

Berseem  or   Egyptian    Clover. 

Harvesting  and  Packing  Grapes  in 
California. 

Machines  for  Coating  Seed  Wheat  with 
Copper    Carbonate    Dust. 

Fruit    Juice    Concentrates. 

Crop  Sequences  at  Davis. 

Cereal  Hay  Production  in  California. 
Feeding  Trials  with  Cereal  Hay. 

Bark   Diseases   of   Citrus  Trees. 

The  Mat  Bean  (Phaseolus  aconitifo- 
lius). 

Manufacture  of  Roquefort  Type  Cheese 
from   Goat's   Milk. 

Orchard  Heating  in  California. 

The  Blackberry  Mite,  the  Cause  of 
Redberry  Disease  of  the  Himalaya 
Blackberry,    and   its   Control. 

The  Utilization  of  Surplus  Plums. 

Cost  of  Work  Horses  on  California 
Farms. 

The  Codling  Moth  in  Walnuts. 

The  Dehydration  of  Prunes. 

Citrus  Culture  in  Central  California. 

Stationary  Spray  Plants  in  California. 

Yield,  Stand  and  Volume  Tables  for 
White  Fir  in  the  California  Pine 
Region. 

Alternaria  Rot  of  Lemons. 

The  Digestibility  of  Certain  Fruit  By- 
products as  Determined  for  Rumi- 
nants. 

Factors  Affecting  the  Quality  of  Fresh 
Asparagus  after  it  is  Harvested. 

Paradichlorobenzene  as  a  Soil  Fumi- 
gant. 

A  Study  of  the  Relative  Values  of  Cer- 
tain Root  Crops  and  Salmon  Oil  as 
Sources  of  Vitamin  A  for  Poultry. 

Planting  and  Thinning  Distances  for 
Deciduous  Fruit  Trees. 

The  Tractor  on  California  Farms. 

Culture  of  the  Oriental  Persimmon 
in    California. 

Poultry  Feeding:  Principles  and 
Practice. 

A  Study  of  Various  Rations  for 
Finishing  Range  Calves  as  Baby 
Beeves. 

Economic  Aspects  of  the  Cantaloupe 
Industry. 

Rice  and  Rice  By-products  as  Feeds 
for   Fattening   Swine. 

Beef   Cattle   Feeding  Trials,    1921-24. 

Cost  of  Producing  Almonds  in  Cali- 
fornia; a  Progress  Report. 

Apricots  (Series  on  California  Crops 
and  Prices). 

The  Relation  of  Rate  of  Maturity  to 
Egg  Production. 

Apple   Growing  in   California. 

Apple  Pollination  Studies  in  Cali- 
fornia. 

The  Value  of  Orange  Pulp  for  Milk 
Production. 

The  Relation  of  Maturity  of  Cali- 
fornia Plums  to  Shipping  and 
Dessert    Quality. 

Economic  Status  of  the  Grape  Industry. 


No. 

87.  Alfalfa. 
117.  The    Selection    and    Cost    of    a    Small 

Pumping  Plant. 
127.  House   Fumigation. 
129.  The  Control  of  Citrus  Insects. 
136.  Melilotua    indica   as    a    Green-Manure 

Crop  for  California. 
144.  Oidium    or    Powdery    Mildew    of    the 

Vine. 
157.  Control  of  the  Pear  Scah. 
164.   Small  Fruit  Culture  in  California. 
166.  The  County  Farm  Bureau. 
170.  Fertilizing    California     Soils    for    the 

1918   Crop. 
173.  The    Construction    of   the   Wood-Hoop 

Silo. 

178.  The  Packing  of  Apples  in   California. 

179.  Factors   of    Importance   in    Producing 

Milk  of  Low  Bacterial  Count. 

202.  County   Organizations  for  Rural   Fire 

Control. 

203.  Peat  as   a  Manure   Substitute. 
209.  The  Function  of  the  Farm  Bureau. 
212.  Salvaging    Rain-Damaged    Prunes. 
215.  Feeding  Dairy  Cows  in  California. 
217.  Methods  for  Marketing  Vegetables   in 

California. 

230.  Testing  Milk,   Cream,   and   Skim  Milk 

for  Butterfat. 

231.  The   Home   Vineyard. 

232.  Harvesting    and    Handling    California 

Cherries   for   Eastern    Shipment. 
234.  Winter  Injury  to  Young  Walnut  Trees 
during  1921-22. 

238.  The  Apricot  in  California. 

239.  Harvesting     and     Handling     Apricots 

and  Plums  for  Eastern  Shipment. 

240.  Harvesting   and    Handling    Pears    for 

Eastern   Shipment. 

241.  Harvesting  and  Handling  Peaches  for 

Eastern   Shipment. 

243.  Marmalade  Juice  and  Jelly  Juice  from 

Citrus  Fruits. 

244.  Central  Wire  Bracing  for  Fruit  Trees. 

245.  Vine  Pruning  Systems. 

248.  Some   Common   Errors   in   Vine  Prun- 

ing and  Their  Remedies. 

249.  Replacing    Missing    Vines. 

250.  Measurement  of   Irrigation   Water  on 

the  Farm. 

252.  Supports  for  Vines. 

253.  Vineyard  Plans. 

254.  The  Use  of  Artificial  Light  to  Increase 

Winter   Egg   Production. 

255.  Leguminous  Plants  as  Organic  Fertil- 

izer   in    California    Agriculture. 

256.  The   Control   of  Wild   Morning   Glory. 

257.  The  Small-Seeded  Horse  Bean. 

258.  Thinning  Deciduous   Fruits. 


CIRCULARS 
No. 


259. 
261. 
262. 
263. 
264. 

265. 
266. 

267. 

269. 
270. 
272. 

273. 
276. 
277. 

278. 

279. 

281. 


282. 

283. 
284. 
285. 
286. 
287. 
288. 
289. 
290. 
291. 

292. 
293. 
294. 
295. 

296. 

298. 

300. 
301. 
302. 
303. 

304. 
305. 
306. 

307. 
308. 
309. 


Pear  By-products. 

Sewing  Grain  Sacks. 

Cabbage  Growing  in  California. 

Tomato  Production  in  California. 

Preliminary      Essentials      to      Bovine 

Tuberculosis  Control. 
Plant  Disease  and  Pest  Control. 
Analyzing     the     Citrus     Orchard     by 

Means  of   Simple  Tree   Records. 
The  Tendency  of  Tractors  to  Rise  in 

Front;   Causes  and  Remedies. 
An  Orchard  Brush  Burner. 
A  Farm  Septic  Tank. 
California  Farm  Tenancy  and  Methods 

of  Leasing. 
Saving  the  Gophered  Citrus  Tree. 
Home  Canning. 
Head,   Cane,   and  Cordon  Pruning  of 

Vines. 
Olive  Pickling  in  Mediterranean  Coun- 
tries. 
The  Preparation  and  Refining  of  Olive 

Oil  in   Southern   Europe. 
The  Results  of  a  Survey  to  Determine 

the  Cost  of  Producing  Beef  in  Cali- 
fornia. 
Prevention  of  Insect  Attack  on  Stored 

Grain. 
Fertilizing  Citrus  Trees  in  California. 
The  Almond  in   California. 
Sweet  Potato  Production  in  California. 
Milk  Houses  for  California  Dairies. 
Potato  Production  in   California. 
Phylloxera  Resistant  Vineyards. 
Oak  Fungus  in  Orchard  Trees. 
The  Tangier  Pea. 
Blackhead  and   Other  Causes  of  Loss 

of  Turkeys  in  California. 
Alkali  Soils. 

The   Basis  of   Grape   Standardization. 
Propagation   of  Deciduous  Fruits. 
The  Growing  and   Handling  of  Head 

Lettuce  in  California. 
Control     of     the     California     Ground 

Squirrel. 
The    Possibilities    and    Limitations    of 

Cooperative  Marketing. 
Coccidiosis  of  Chickens. 
Buckeye  Poisoning  of  the  Honey  Bee. 
The   Sugar  Beet  in  California. 
A  Promising  Remedy  for  Black  Measles 

of  the  Vine. 
Drainage  on  the  Farm. 
Liming  the  Soil. 
A  General  Purpose  Soil  Auger  and  its 

Use  on  the  Farm. 
American   Foulbrood  and  its   Control. 
Cantaloupe  Production  in  California. 
Fruit  Tree  and  Orchard  Judging. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 


19m-ll,'27 


